code: def test_builder_to_backend_nested(self, compute_unit, backend):
      if backend.backend == "neuralnetwork":
          pytest.xfail(
              "rdar://96862073 (test_control_folw::TestWhileLoop::test_builder_to_backend_nested failing on nnv1)"
          )
  
      input_placeholders = {
          "x": mb.placeholder(shape=(1,)),
          "y": mb.placeholder(shape=(1,)),
      }
  
      def build(x, y):
          # i, j = x, y
          # while i < j:
          #   while 2*i < i+2:
          #     i += 1
          #   i += 2
          # return i, j
  
          # Create const outside of while loop for testing purpose
          two = mb.const(val=[2.0], name="const_two")
          one = mb.const(val=[1.0], name="const_one")
  
          def cond2(i):
              return mb.less(x=mb.mul(x=two, y=i), y=mb.add(x=i, y=two))
  
          def body2(i):
              return mb.add(x=i, y=one)
  
          def cond1(i, j):
              return mb.less(x=i, y=j)
  
          def body1(i, j):
              new_i = mb.while_loop(
                  _cond=cond2, _body=body2, loop_vars=(i,)
              )
              return mb.add(x=new_i, y=two), j
  
          return mb.while_loop(
              _cond=cond1, _body=body1, loop_vars=(x, y)
          )
  
      input_values = {
          "x": np.array([0], dtype=np.float32),
          "y": np.array([10], dtype=np.float32),
      }
  
      expected_output_types = [
          (1, types.fp32),
          (1, types.fp32),
      ]
  
      expected_outputs = [
          np.array([10], dtype=np.float32),
          np.array([10], dtype=np.float32),
      ]
      run_compare_builder(
          build,
          input_placeholders,
          input_values,
          expected_output_types,
          expected_outputs,
          compute_unit=compute_unit,
          backend=backend,
      )
  
imports: import itertools
  import numpy
  import pytest
  from coremltools.converters.mil.mil import Builder
  from coremltools.converters.mil.mil import get_new_symbol, types
  from coremltools.converters.mil.mil.ops.tests.iOS14 import backends
  from coremltools.converters.mil.mil.ops.tests.testing_utils import UNK_SYM, construct_inputs_from_placeholders, run_compare_builder
  from coremltools.converters.mil.testing_reqs import compute_units
  from coremltools.converters.mil.testing_utils import random_gen, ssa_fn
label_desc: Use image node_id 3 for calling the TestWhileLoop obj's underlying member method code with example usage: obj.test_builder_to_backend_nested(compute_unit, backend) and returns: mb, mb, mb, mb, mb,  j